1. Field of the Invention
The present invention relates to an optical fiber array coupled to a semiconductor laser diode array and a method of producing the optical fiber array, and more particularly, to an optical fiber array in which a plurality of optical fibers, each having a lens formed integrally at an end thereof, are arrayed in such a manner that they project from an end face of a fiber array block by substantially the same length, and a method of producing the optical fiber array.
2. Description of the Related Art
A conventional light-emitting module incorporated in an optical communications system comprises a laser diode (hereinafter referred to as "LD") serving as a light source, and a lens interposed between the LD and an optical fiber for converging the laser beam onto the core of the optical fiber. To make good use of the energy of the LD, the module is required to have a high coupling efficiency which is the ratio (%) of the amount of light incident on the optical fiber to the amount of light emitted from the LD. To this end, the light-emitting module is assembled with the optical axes of the LD, lens, and optical fiber aligned with each other, so as to achieve a maximum coupling efficiency between the LD and the optical fiber.
Recently, an optical fiber has been proposed in which a lens is formed directly on an end thereof (hereinafter referred to as "lensed optical fiber"). In this type of optical fiber, the fiber end itself functions as a lens. Consequently, the number of parts constituting the module is lessened. Also, the number of operations required for the optical axis alignment during manufacture can be reduced, whereby the cost is cut down.
The lensed optical fiber is produced in the manner described below, for example.
First, an optical fiber, from which a jacket has been removed, is heated locally by heating means such as a burner, with a tensile force applied thereto, whereby the heated portion is extended. When the outer diameter of the heated portion is decreased to about 10 .mu.m or less, application of the tensile force is stopped. After the diameter-reduced part is cut with a cutter, the cut end of the optical fiber is again heated by the burner for fusion. As the fiber end is melted, its shape becomes semispherical due to surface tension, and this semispherical end functions as a lens.
Thus, the lensed optical fiber has a semispherical lens at an end thereof, as well as a taper portion of a certain length whose diameter gradually increases with distance from the semispherical end.
A conventional light-emitting module using the lensed optical fiber has an arrangement shown in FIG. 16, for example, as disclosed in Unexamined Japanese Utility Model Publication (KOKAI) No. 3-6612. As illustrated, a bare LD 1 is arranged within a package 2 having an upper open end, and a lensed optical fiber 3 is inserted through a wall of the package 2 in such a manner that a lens 3a at the fiber end faces the light-emitting surface of the LD 1 with a space of about 10 .mu.m therebetween. To protect the LD 1 against oxidation and moisture, a cover 4 is fitted on the open end of the package 2, and the lensed optical fiber 3 is firmly secured to the wall by solder 5, so that the package 2 has an airtight structure.
Recently, there is an increasing demand for a light-emitting module capable of connecting an LD array, which includes a plurality of LDs (light sources), to an optical fiber array, which includes a plurality of optical fibers arranged in a fiber array block, by means of a lens array including a plurality of lenses, thereby collectively coupling the LDs to the respective optical fibers.
In such a light-emitting module, the coupling efficiency between the individual arrays is preferably as high as possible. Also, the emission power of the individual optical fibers arranged in the fiber array needs to be identical.
Thus, when producing a light-emitting module, it is necessary that the dimensional accuracy of each array be high and that the optical axes of the LDs, lenses, and optical fibers be aligned for each optical path.
In the case where this type of light-emitting module is produced using the lensed optical fibers, preliminary work is required wherein a plurality of lensed optical fibers are arrayed and fixed to a fiber array block to obtain an optical fiber array.
In this case, if the ends of the lensed optical fibers are positioned irregularly with respect to the corresponding LDs of the LD array, there occurs a variation in the distances from the LDs to the corresponding fiber ends when the LD array is coupled to the optical fiber array. Consequently, a plurality of optical systems each comprising an optical fiber and an LD associated therewith will have different coupling efficiencies, lowering the reliability of the light-emitting module.
Further, since the lensed optical fiber has a semispherical lens at an end thereof, positioning the lens surfaces of all fibers in alignment requires significant labor, unlike the conventional optical fibers whose end faces are perpendicular to their optical axes.
Generally, the fiber array block is made of a synthetic resin such as epoxy resin, and when a light-emitting module is assembled, the LD array and the optical fiber array are placed close to each other. Accordingly, during operation of the light-emitting module, gas is emitted from the synthetic resin forming the optical fiber array, due to heat generated by the LD array, and contaminates the LD array.